In every industrial field, various devices for press fitting, presswork or clamping of an object have been used, which utilize a power source such as man power, a pneumatic cylinder or an electric motor.
In the case of a small pressing machine for example, many pressing machines that use man power have a mechanism for operating a lever handle by man power so as to rotate a pinion gear that is coupled to a shaft of the lever handle for applying a rectilinear thrust to a rack shaft. Other than this mechanism, a cam mechanism or a link mechanism is used for amplifying a force so as to obtain a thrust. Although the pressing machine that uses man power can be manufactured with low cost because of a simple mechanism and structure, it is not suitable for a stable work because the pressing force depends on man power. In addition, the use of man power means consuming a labor cost that is most expensive among fixed manufacturing costs, which goes against the recent trend toward a labor-saving device or a motorized device. For this reason, a pressing device utilizing a pneumatic cylinder or an electric motor has been used in many cases recently.
A pressing device utilizing a pneumatic cylinder has advantages that a stable pressing force can be obtained by supplying compressed air having controlled pressure to the cylinder and that it can be manufactured with relatively low cost because of its simple mechanism, so it is used in many cases. However, it needs compressed air as a power source, and an air compressor has to be installed. In addition, necessary power for a press fitting or caulking work depends on the pressing force and the traveling speed at a work position, but the thrust of the pneumatic cylinder is determined by a product of a sectional area of the cylinder and pressure of supplied air. Therefore, the energy of the compressed air corresponding to the sum of a volume of an idle running distance to the work position and a volume of a return stroke is consumed in vain.
On the other hand, a pressing device utilizing an electric motor obtains a necessary thrust by converting a rotational motion into a linear motion after amplifying an output torque of the electric motor by a speed reducer or the like so that the pressing force at the work position is increased. However, only reducing the speed simply causes decrease of the number of rotation so that it takes time to move the idle running distance.
There are various methods and devices that have been developed for reducing energy consumption and shortening cycle time in a power transmission device that uses a pneumatic cylinder or an electric motor. For example, as a power transmission mechanism that utilizes an electric motor, there are “power transmission method and device for converting rotational motion into rectilinear motion” described in Japanese unexamined patent publication No. 5-164209 and “machine tool” described in Japanese unexamined patent publication No. 11-151632.
A technique that is common to descriptions in the above-mentioned documents is to obtain a necessary pressing force by moving at high speed and low thrust during an interval of the idle running distance, by switching speed reducers by a clutch or the like at the work position for performing press fitting or caulking so that speed reduction and thrust augmentation are performed. According to each of these conventional techniques, the mechanism becomes complicated so it is difficult to provide an inexpensive device.
An object of the present invention considering the above-mentioned problem is to realize an inexpensive power transmission method and device that has a simple mechanism for switching speeds of linear motion and for amplifying a thrust in an autonomous manner.